Heating, ventilation, and/or air conditioning (HVAC) systems often include a furnace in many commercial and residential applications for heating and otherwise conditioning interior spaces. Because the efficiency of a furnace in an HVAC system often relies on the heat transfer efficiency of a primary and/or secondary heat exchanger in a furnace, some HVAC systems comprise furnaces with add on baffles and/or alternative flowpaths that are configured to redirect airflow into contact with the heat exchangers in order to increase efficiency of the furnace and subsequently the HVAC system.